1. Field
This application relates generally to wireless communication and more specifically, but not exclusively, to improving communication performance.
2. Introduction
A wireless communication network may be deployed over a defined geographical area to provide various types of services (e.g., voice, data, multimedia services, etc.) to users within that geographical area. In a typical implementation, access points (e.g., corresponding to different cells) are distributed throughout a network to provide wireless connectivity for access terminals (e.g., cell phones) that are operating within the geographical area served by the network.
As the demand for high-rate and multimedia data services rapidly grows, there lies a challenge to implement efficient and robust communication systems with enhanced performance. To supplement conventional network access points (e.g., macro access points), small-coverage access points (e.g., with transmit power of 20 dBm or less) may be deployed to provide more robust coverage for access terminals. For example, a small-coverage access point installed in a user's home or in an enterprise environment (e.g., commercial buildings) may provide voice and high speed data service for access terminals supporting cellular radio communication (e.g. CDMA, WCDMA, UMTS, LTE, etc.).
Conventionally, small-coverage access points may be referred to as, for example, femtocells, femto access points, home NodeBs, home eNodeBs, or access point base stations. Typically, such small-coverage access points are connected to the Internet and the mobile operator's network via a DSL router or a cable modem. For convenience, small-coverage access points may be referred to as femtocells or femto access points in the discussion that follows.
In practice, a tradeoff may need to be made between providing adequate femtocell radiofrequency (RF) coverage for users of the femtocell and limiting interference to other access points (e.g., nearby macrocells) and to users of these other access points. For example, for a femtocell that is deployed indoors, it may be desired to provide good indoor RF coverage throughout the entire building, while limiting outdoor leakage that would otherwise interfere with uplink and/or downlink communication of nearby access points.
Interference is caused in various ways. Due to scarcity of spectrum resources, femtocells often share the frequency channels used by the macrocells or are deployed on adjacent channels with a limited guard band. In either of these cases, femtocells and macrocells may interfere with each other on these channels.
Another cause of interference is beacon transmission. Macrocells typically operate on multiple frequencies. To attract the macrocell users to its service channel, a femtocell radiates beacons (e.g., comprising pilot, paging, and synchronization channels) on these macrocell frequencies. These beacons create interference on the macro network if there is no active hand-in support between the macrocell and femtocell. This interference can affect the voice call quality of users receiving active service on the macrocell frequency and, in some cases, lead to call drops.
In view of the above, it is desirable to calibrate femtocell service channel transmit power and femtocell beacon channel transmit power to provide adequate coverage while mitigating interference to the macro network. In some aspects, the desired power levels depend on the indoor area and propagation environment, as well as the prevalent macro network conditions. For example, traditional interference mitigation techniques may use a Network Listen Module (NLM) to detect surrounding macrocell channel quality and calibrate femtocell transmit power based on the detected channel quality. In general, the NLM includes receiver components that are configured to acquire forward link signals transmitted by nearby access points. However, these methods are generally based on simplistic assumptions regarding the coverage area and macrocell interference variation and, as a result, may not provide a desired level of coverage. Thus, there is a need for improved RF coverage control for wireless networks.